(1) Field of the Invention
The present invention relates to a scan type image display device that uses a scan mirror to two-dimensionally scan the screen with an optical beam to thereby display an image on the screen.
(2) Description of the Related Art
Recently, a scan type image display device has been proposed which modulates the intensity of an optical beam emitted by a laser optical source according to an image signal and two-dimensionally scans the screen with the optical beam, thereby displaying an image using the afterimage effect. The micro electro mechanical systems (MEMS) mirror is known as a scan unit employed in such scan type image display devices. The MEMS mirror is such that its mirror surface rotates to two-dimensionally scan the screen with an optical beam emitted from the light source (refer to, for example, JP-A-2006-189573 and JP-A-2009-533715). The MEMS mirror is hereinafter referred to as a “scan mirror”.
FIG. 6 of JP-A-2006-189573 and FIG. 20 of JP-A-2009-533715 each illustrate a configuration in which a beam is incident on the scan mirror in a nearly vertical direction (the incident angle is approximately 0) so as to enlarge the deflection angle of the beam relative to the rotational angle of the mirror surface. In this case, light incident on the scan mirror and light reflected by the scan mirror take a common optical path. Therefore, the optical beam to be projected is polarized into a linear polarized beam, and a polarized beam splitter (PBS) and a quarter wave plate are arranged in the optical path to thereby separate the paths of the incident light and the reflected light.